This project continues an extensive analysis of the structure of taste organs and related receptors. Emphasis has been and continues to be on mammalian taste buds, particularly those of the rabbit. During the next year the histochemical exploration at the electron microscope level of rabbit foliate taste buds will be a major aim. This will include enzyme histochemistry, the use of several relatively non- specific reagents such as ruthenum red, P.T.A. and KMnO4, as well as autoradiography after H3 thymidine administration. In an adjunctive study, the ultrastructure of the olfactory receptors of a bee, a wasp and a mosquito are being compared. Trophic factors involved in taste bud growth and maintenance will be studied in catfish by noting acute and long-term effect of denervation. These will be studied both at the light and electron microscopic level.